Recently, an ionomer resin has widely been used as a base resin for a cover of a golf ball (e.g. Japanese Laid-Open Patent Publication No. 49-27093). Particularly, the ionomer resin is exclusively used in a two-piece golf ball using a solid core.
This is because the ionomer resin is superior in durability, cut resistance and resilience performances, and, further, it is easily processed and inexpensive in comparison with other base resin for the cover.
However, the ionomer resin is inferior in hit feeling and control properties (easiness of applying spin on a ball) in comparison with a balata (transpolyisoprene) used as the base resin for the cover of the thread wound golf ball since the ionomer resin has considerably high hardness and stiffness.
Therefore, an attempt to improve the hit feeling and control performances by softening the ionomer resin with various means has been made.
For example, Japanese Laid-Open Patent Publication Nos. 1-308577 and 5-3913 suggest that a high-rigid ionomer resin is softened by blending (mixing) a soft ionomer resin, obtained by neutralizing a terpolymer of .alpha.-olefin, unsaturated carboxylic acid (e.g. acrylic acid, methacrylic acid, etc.) and acrylate with sodium or zinc ion, to improve the hit feeling and control properties.
However, even if the soft ionomer resin as described above is blended, the hit feeling similar to that of the golf ball with the balata cover have still to be obtained. Further, blending of the soft ionomer resin is accompanied by deterioration of resilience performances and flying performances and, therefore, satisfactory results have not been obtained.
As described above, the ionomer resin cover is inferior in hit feeling and control properties in comparison with the thread wound golf ball with the balata cover mainly used for thread wound golf balls, because the ionomer resin has high hardness and stiffness. Further, satisfactory results have not been obtained in an attempt to improve the hit feeling and control properties by softening the ionomer resin.